Print on demand heat blanket system

ABSTRACT

A heat blanket system including a blanket including a first sub-area and a second sub-area. The heat blanket system also includes heating elements printed on the blanket. First spacings between first ones of the heating elements in the first sub-area varies relative to second spacings between second ones of the heating elements in the second sub-area. The first spacings and the second spacings vary according to a design. The design is configured for use on a uniquely defined rework area on a uniquely defined composite material object including a third area including a heat sink region and a fourth area including a non-heat sink region. The first sub-area is sized and dimensioned to be placed over the third area. The second sub-area is sized and dimensioned to be placed over the fourth area.

RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 16/860,243, filed Apr. 28, 2020, the entirety of which is herebyincorporated by reference.

FIELD

The one or more embodiments are in the field of composite materialreworking and more particularly in the field of heating blankets usedfor reworking composite materials.

BACKGROUND

Inconsistencies may sometimes form in composite material objects. An“inconsistency” is defined as any measurable feature of a compositematerial which lies outside a pre-determined normative engineeringtolerance.

The composite material may be reworked in order to remove or mitigatethe inconsistency. “Reworking” a composite material is defined as anyprocedure performed on the composite material to remove or mitigate theinconsistency. The term “mitigate the inconsistency” is defined asbringing the composite material object into pre-determined engineeringtolerances.

Reworking a composite material may involve adding a liquid compositeresin, a pre-preg tape (a “pre-preg” is pre-impregnated composite fiberswhere a thermoset polymer matrix material, such as epoxy, or athermoplastic resin is already present), a composite patch, or someother pre-cured composite material to the area of the inconsistency. Thepre-cured material is then bonded to the parent structure, mitigatingthe inconsistency using a film or paste adhesive. The pre-curedcomposite material and adhesive are heated as part of a curing process.

In some cases, heating may be accomplished using a heating blanket.However, when the pre-cured composite material has varying thickness, oris disposed over components in the object that act as heat sinks, thennon-uniform heating may occur within the pre-cured composite material.The non-uniform heating may create inconsistencies during the cureprocess.

SUMMARY

The one or more embodiments includes a heat blanket system. The heatblanket system includes a blanket including a first sub-area and asecond sub-area. The heat blanket system also includes heating elementsprinted on the blanket. First spacings between first ones of the heatingelements in the first sub-area varies relative to second spacingsbetween second ones of the heating elements in the second sub-area. Thefirst spacings and the second spacings vary according to a design. Thedesign is configured for use on a uniquely defined rework area on auniquely defined composite material object including a third areaincluding a heat sink region and a fourth area including a non-heat sinkregion. The first sub-area is sized and dimensioned to be placed overthe third area. The second sub-area is sized and dimensioned to beplaced over the fourth area.

Other aspects of the invention will be apparent from the followingdescription and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a heat blanket system disposed on a rework area, inaccordance with one or more embodiments;

FIG. 2 illustrates a method for manufacturing and using aprint-on-demand heat blanket system, in accordance with one or moreembodiments;

FIG. 3 illustrates a method for reworking an aircraft using aprint-on-demand heat blanket system, in accordance with one or moreembodiments;

FIG. 4 illustrates a section of a composite material object, including arework area, in accordance with one or more embodiments;

FIG. 5 illustrates a system for generating a print-on-demand heatblanket system, in accordance with one or more embodiments;

FIG. 6 illustrates a specific example of a print-on-demand heat blanketsystem, and a method of use, in accordance with one or more embodiments;

FIG. 7 illustrates application of the specific example of theprint-on-demand heat blanket system shown in FIG. 6 , in accordance withone or more embodiments;

FIG. 8 illustrates an aircraft panel having with a rework area includingan inconsistency, in accordance with one or more embodiments;

FIG. 9 illustrates an alternative view of the aircraft panel of FIG. 8 ,in accordance with one or more embodiments;

FIG. 10 illustrates a cross-section of the aircraft panel of FIG. 8 , inaccordance with one or more embodiments;

FIG. 11 illustrates a part of a heating simulation as part of a processfor producing a heating model for the panel shown in FIG. 8 , inaccordance with one or more embodiments;

FIG. 12 illustrates another part of the heating simulation in FIG. 11 aspart of a process for producing a heating model for the panel shown inFIG. 8 , in accordance with one or more embodiments;

FIG. 13 illustrates a heating model for the panel shown in FIG. 8 , inaccordance with one or more embodiments;

FIG. 14A illustrates a heat density map for a thermal blanket generatedfrom the heating model in FIG. 13 , in accordance with one or moreembodiments;

FIG. 14B illustrates a heat density map for a thermal blanket generatedfrom the heating model in FIG. 13 , in accordance with one or moreembodiments;

FIG. 15 illustrates an aircraft manufacturing and service method, inaccordance with one or more embodiments; and

FIG. 16 illustrates an aircraft, in accordance with one or moreembodiments.

DETAILED DESCRIPTION

Specific embodiments of the invention will now be described in detailwith reference to the accompanying figures. Like elements in the variousfigures are denoted by like reference numerals for consistency.

In the following detailed description of embodiments of the invention,numerous specific details are set forth in order to provide a morethorough understanding of the invention. However, it will be apparent toone of ordinary skill in the art that the invention may be practicedwithout these specific details. In other instances, well-known featureshave not been described in detail to avoid unnecessarily complicatingthe description.

Throughout the application, ordinal numbers (e.g., first, second, third,etc.) may be used as an adjective for an element (i.e., any noun in theapplication). The use of ordinal numbers is not to imply or create anyparticular ordering of the elements nor to limit any element to beingonly a single element unless expressly disclosed, such as by the use ofthe terms “before”, “after”, “single”, and other such terminology.Rather, the use of ordinal numbers is to distinguish between theelements. By way of an example, a first element is distinct from asecond element, and the first element may encompass more than oneelement and succeed (or precede) the second element in an ordering ofelements.

The term “about,” when used with respect to a physical property that maybe measured, refers to an engineering tolerance anticipated ordetermined by an engineer or manufacturing technician of ordinary skillin the art. The exact quantified degree of an engineering tolerancedepends on the product being produced and the technical property beingmeasured. For a non-limiting example, two angles may be “aboutcongruent” if the values of the two angles are within ten percent ofeach other. However, if an engineer determines that the engineeringtolerance for a particular product should be tighter, then “aboutcongruent” could be two angles having values that are within one percentof each other. Likewise, engineering tolerances could be loosened inother embodiments, such that “about congruent” angles have values withintwenty percent of each other. In an example of a temperaturedifferential, “about a uniform temperature” refers to a range oftemperatures about an ideal temperature for a particular application.Thus, in a more particular, but non-limiting, example, an “about uniformtemperature” could be 200 degrees Fahrenheit plus or minus ten degreesFahrenheit throughout a composite material, assuming that a temperaturevariance of ten degrees Fahrenheit in different areas of the compositematerial was within the pre-determined engineering tolerance. In anycase, the ordinary artisan is capable of assessing what is an acceptableengineering tolerance for a particular product, and thus is capable ofassessing how to determine the variance of measurement contemplated bythe term “about.”

In general, embodiments of the invention relate to print-on-demand heatblanket systems specifically designed to be used with respect to curinga particular uncured composite patch, or other uncured compositematerial, applied to a specific area of rework on a specific object madeof a composite material. In other words, the one or more embodimentsprovide for a heat blanket system, and method for manufacturing and use,specifically tailored for reworking a specific inconsistency on aspecific composite material object.

As used herein, a “heat blanket system” is defined as a blanket, adesignated pattern of heating elements disposed on or in the blanket,and any other components attached to the blanket (such as, but notlimited to, leads, circuitry, power sources, transformers, etc.). The“heat blanket system” of the one or more embodiments provides for a“heat blanket system” that has a custom array (i.e., specificallydesigned for a particular rework project) of heating elements, plus anycomponents attached to the blanket.

Heating blankets, such as but not limited to electric blankets, are usedfor heating and curing composite patches and other composite material.Heating blankets may be procured from vendors in a variety of sizes andare typically round or rectangular in shape.

Procuring a pre-made, off-the-shelf heating blanket can result inchallenges when reworking an area of a composite object, such as aportion of an aircraft. One challenge is that the sizes and shapes ofinconsistencies vary widely. A technician may attempt to anticipate whatsize blanket will be useful for reworking a variety of inconsistencies.However, the technician may significantly modify the rework approachbased on the size and shape of the available blankets. If the availableblankets cannot be adapted to the application, then a new blanket mustbe ordered. The typical lead time for a custom heat blanket can be amonth or more. In the case of an aircraft to be reworked, the delay mayresult in loss of service time for the aircraft, which in turn directlytranslates into lost revenue and profit for the aircraft operator.

Another challenge of using an off-the-shelf heating blanket is that suchheating blankets have heating elements disposed at a uniform spacingthroughout the heating blanket. Thus, the off-the-shelf heating blanketproduces a uniform heat output, or watt density, for the area of theblanket. As a result, when the blanket is energized, the blanket emitsthe same amount of heat over the surface of the blanket. A challengeassociated with uniform heating is that many reworking projects foraircraft will not have uniform thermal requirements. For example, skinthicknesses can change over multiple sections of an aircraft in which aninconsistency is located. Furthermore, the inconsistency may be locatedover integral stiffeners or a honeycomb core which underly certainportions of the aircraft skin in which the inconsistency is located. Asa result, when an off-the shelf heating blanket emits a uniform amountof heat over the rework region, temperatures will undesirably varywidely across the rework area being cured (e.g., cooler under thestiffeners and warmer where the skin is thinner). However, most reworkprocesses specify that the curing temperature remain within apre-determined threshold throughout the composite patch. For example,the temperature difference throughout a composite patch might bespecified to remain within ten degrees Fahrenheit above or below thecure temperature. In other words, what is desirable is not that theblanket emits a uniform amount of heat, but rather that the compositepatch maintain an even elevated temperature throughout the compositepatch, regardless of thickness differences in the patch, and regardlessof the presence of heat sinks in the underlying structure.

To mitigate the non-uniform patch temperatures, localized insulation maybe placed on a vacuum bag to warm areas within the patch that are belowthe pre-defined temperature threshold. A challenge with using localizedinsulation is that the insulation and cure are constantly monitored andmanaged for the duration of the curing process. Insulation is added orremoved throughout curing to prevent thermocouples from becoming too hotor cold. Thus, the monitoring process is burdensome, and error prone.Errors may result in having to redo a rework project. Redoing a reworkproject is undesirable both in terms of expense and the time taken toperform the additional rework project. In some cases, the part beingreworked may be discarded when an error arises, further increasing costand rework time.

The one or more embodiments address these and other challenges byproviding for a print-on-demand (POD) heat blanket system that isspecifically tailored to a specific rework project. The POD heat blanketsystem emits non-uniform heating across the dimensions of the POD heatblanket system in order to compensate for composite patch areas thatrequire more or less heat to maintain the temperature differencethreshold within the composite patch. Areas of the rework that requireadditional heating, due to increased patch thickness or the presence ofheat sinks in the underlying composite part, receive additional heatingthrough greater heating element density. In turn, areas of the reworkthat require less heating, due to decreased patch thickness or theabsence of heat sinks in the underlying composite part, will receiveless heating through lower heating element density.

The term “heating element density” is defined as a measurement of thespacing, or distance, between heating elements. Thus for example, afirst blanket with a higher heating element density relative to a secondblanket will have more heating elements per inch than the secondblanket.

The POD heat blanket system of the one or more embodiments has severalbenefits. The POD heat blanket system achieves improved curing resultsby maintaining a more uniform heating temperature throughout the reworkarea, i.e., by avoiding undesirable temperature variations in the reworkarea. The POD heat blanket system may be manufactured at the workshopperforming the rework project, thereby increasing the speed of therework process and decreasing the time an aircraft is out of service.The POD heat blanket system reduces costs by allowing a technician tomanufacturing or procure the specific heat blanket system to be used fora particular rework project, instead of procuring many off-the-shelfheating blankets of varying shapes and sizes for selective use indifferent rework projects.

Attention is now turned to the figures. FIG. 1 illustrates a heatblanket system disposed on a rework area, in accordance with one or moreembodiments. The heat blanket system (100) may be laid on, cover, orotherwise be disposed on the rework area (102) of a composite materialobject (104). The rework area (102) is a portion of the compositematerial object (104) that is to be reworked. The rework area (102) maybe larger or smaller than the inconsistency (not shown) present in or onthe composite material object (104). In many cases, the rework area(102) is larger than the inconsistency.

The heat blanket system (100) is divided into multiple sub-areas,including a first sub-area (106) and a second sub-area (108). Eachsub-area is a portion of heat blanket system (100). Each sub-area may bepart of one contiguous material that forms the heat blanket system(100), or may be discontinuous from some portion of the heat blanketsystem (100).

The heat blanket system (100) itself is a substrate which may be formedfrom a variety of materials, such as paper, polyethylene terephthalate(PET), or poly (4,4′-oxydiphenylene-pyromellitimide) (which is marketedby the DuPont Company under the trademark KAPTON®), or other polymerfilms. Additional materials are added to the substrate, such as one ormore of heating elements, thermal sensors, thermocouples, etc., asdescribed further below. Additional layers also may be added to thesubstrate. For example, either side of the substrate may be laminatedwith one or more dielectric layers or films to provide electricalinsulation for any electrical elements disposed on the substrate. Thus,a first side of the substrate may have a first dielectric or insulativelayer, and a second side of the substrate may have a second dielectricor insulative layer disposed opposite the first side of the substrate.Optionally, the side of the heat blanket placed against theinconsistency may be a one-side bondable film. This option allows theblanket to be placed directly on the rework surface without anadditional layer of release film that would normally be present.

Each sub-area of the heat blanket system (100) is designed to be placedon a specific area of the composite material object (104) in the reworkarea (102). Thus, for example, the first sub-area (106) of the heatblanket system (100) overlies a third area (110) of the rework area(102). Similarly, for example, the second sub-area (108) of the heatblanket system (100) overlies a fourth area (112) of the rework area(102).

Heating elements may be placed on the heat blanket system (100) by avariety of methods, such as by deposition or by printing. Printingmethods include, but are not limited to, three dimensional printing,inkjet printing, screen printing, atomized jetted deposition, plasmaflame spray, etc. The heating elements may be electrically resistiveheating elements, such as electrically conductive or resistive inks, ormay be some other type of heating element, such as fluid tubes.

Each sub-area of the heat blanket system (100) may have a different setof heating elements. For example, the third area (110) of the heatblanket system (100) may have disposed thereon first heating elements(114). Similarly, the fourth area (112) of the heat blanket system (100)may have disposed thereon second heating elements (116).

Each set of heating elements may have different spacings betweenindividual heating elements. Thus, for example, the first heatingelements (114) may have first spacings (118). Similarly, the secondheating elements (116) may have second spacings (120). As used herein,“spacing” refers to the distance between individual heating elements. Inthis example, the first spacings (118) is less than the second spacings(120). As a result, the density of the first heating elements (114) isgreater than the density of the second heating elements (116).

Accordingly, the total heat produced by the first heating elements (114)in the first sub-area (106) over the third area (110) is greater thanthe total heat produced by the second heating elements (116) in thesecond sub-area (108) over the fourth area (112). However, due to thedifferential heating needs in the third area (110) relative to thefourth area (112), the temperature variation within the rework area(102) as a whole will remain within the threshold temperature range. Inthe arrangement shown in FIG. 1 , the third area (110) of the reworkarea (102) is a heat sink, and the second sub-area (108) of the reworkarea (102) is a non-heat sink region.

The spacings of the heating elements are part of a design that isselected based on a heat model generated for the rework area (102) ofthe composite material object (104). The heat model is a map whichindicates how much heat is to be applied over any given section of therework area (102) in order to maintain the rework area (102) within athreshold temperature difference. Thus, in this example, more heat is tobe applied in the third area (110) relative to the fourth area (112) inorder to maintain the desired threshold temperature differentialthroughout the rework area (102) during curing of a composite patch (seeFIG. 7 ).

An example of the heat model is shown with respect to FIG. 13 . The heatmodel (1300) may be used to generate a design for the heat blanketsystem (100) which will be used to manufacture the heat blanket system(100) shown in FIG. 1 . Specifically, the design specifies the firstspacings (118) for the third area (110) and the second spacings (120)for the second sub-area (108). The design also may specify the type ofheating elements used, and the shape of the heating elements used. Thedesign may also specify the shape of the various areas and/or theheating elements of the heat blanket system (100). Thus, while FIG. 1shows rectangular, evenly spaced heating elements and areas, the shapesand sizes of the third area (110), the fourth area (112), the firstheating elements (114), and the second heating elements (116) may varyin accordance with the heating predicted by the heat model (1300) to beused for various uniquely-defined sub-areas of the rework area (102).

Thus, the one or more embodiments provide for a heat blanket system(100) having a first sub-area (106) and a second sub-area (108). Theheating elements are printed on the heat blanket system (100). Firstspacings (118) between first ones of the heating elements (first heatingelements (114)) in the first sub-area (106) varies relative to secondspacings (120) between second ones of the heating elements (secondheating elements (116)) in the second sub-area (108). The first spacings(118) and the second spacings (120) vary according to a design. Thedesign is configured for use on a uniquely defined rework area on auniquely defined composite material object (104) having a third area(110) including a heat sink region and a fourth area (112) including anon-heat sink region. In other embodiments, the arrangement may bereversed or varied. The first sub-area (106) is sized and dimensioned tobe placed over the third area (110). The second sub-area (108) is sizedand dimensioned to be placed over the fourth area (112). The firstspacings (118) may be less than the second spacings (120), or viceversa.

The heat blanket system (100) may be provided with additional features.For example, the heat blanket system (100) may include one or morethermal sensors, such as first thermal sensor (122) and second thermalsensor (124). Each thermal sensor may be a thermistor, thermometer, orany other heat sensor suitable for printing or deposition on the heatblanket system (100).

Each thermal sensor senses heat in a particular region of the reworkarea (102). Thus, for example, the first thermal sensor (122) may sensea first temperature in the third area (110) of the rework area (102).Similarly, the second thermal sensor (124) may sense a secondtemperature in the fourth area (112) of the rework area (102).

Still other features may be provided. For example, perforations (126)may be disposed through the heat blanket system (100) at variousselected portions of the heat blanket system (100). The perforations(126) are provided, in one embodiment, in order to vent gases emitted bythe curing composite material in the rework area (102). In someembodiments, the perforations could affect the heating applied to thevarious areas in the rework area (102). The heat model (1300) may takeinto account such heating variations, if significant, and the spacingsof the heating elements in the various areas of the heat blanket system(100) may be modified accordingly.

The perforations (126) may be of a variety of shapes and sizes, and maybe disposed at different densities (spacings) relative to each other indifferent areas of the heat blanket system (100). Thus, for example,first perforation (128) is shown as a circle, while second perforation(130) is shown as a square, while additional perforations (132) areshown as circles smaller than the first perforation (128). While theperforations (126) are shown outside of the first sub-area (106) and thesecond sub-area (108) of the heat blanket system (100), the perforations(126) may be disposed within the first sub-area (106) and/or the secondsub-area (108), or other portions of the heat blanket system (100).

Additional features may be added to the heat blanket system (100). Forexample, a control circuit (134) may be printed or otherwise depositedon the heat blanket system (100). The control circuit (134) may be anapplication specific integrated circuit (ASIC) or other electricalcircuit specifically designed for the heat blanket system (100) for usefor the rework area (102). The control circuit (134) may be used tocontrol or modify power delivered to the first heating elements (114)and/or the second heating elements (116) based on signals received bythe wireless transmitter, such as signals received from a remotecomputer. The control circuit (134) may also be used to monitor thefirst thermal sensor (122) and the second thermal sensor (124), and/orto calculate a difference in temperature as measured by the firstthermal sensor (122) and the second thermal sensor (124).

The control circuit (134) may also control other devices printed orotherwise disposed on the heat blanket system (100). For example, analert device (136) may be printed or otherwise disposed on the heatblanket system (100). The control circuit (134) may be programmed tocause the alert device (136) to issue an alert when a difference intemperature measured by the first thermal sensor (122) and the secondthermal sensor (124) exceeds a threshold. The alert may take the form ofan audio alarm, a visual cue (such as a blinking light emitting diode(LED)), etc.

In another example, a wireless transmitter (138) may be printed orotherwise disposed on the heat blanket system (100). The wirelesstransmitter (138) may transmit temperature measurements generated by thefirst thermal sensor (122) and/or the second thermal sensor (124). Thewireless transmitter (138) may also transmit an alert to a remotecomputer when the control circuit (134) determines that a difference intemperature between the first thermal sensor (122) and the secondthermal sensor (124) exceeds the threshold.

The wireless transmitter (138) may also be in communication with acomputer (140). The computer (140) may be programmed to monitor and/orcontrol various features of the heat blanket system (100), including thepower source (142) described below. For example, the computer (140) mayrecord temperature measurements from the first thermal sensor (122)and/or the second thermal sensor (124). The computer (140) may take theplace of some of the functions of the control circuit (134), such as tomonitor a difference between the measurements of the first thermalsensor (122) and the second thermal sensor (124), or to generate analert. The computer (140) may also be the same computer that generatesthe heat model (1300) and/or the design of the heating elements, asdescribed respect to the example shown in FIG. 8 through FIG. 14B. Insome embodiments, the computer (140) may be miniaturized and disposeddirectly on the heat blanket system (100), possibly in place of thecontrol circuit (134).

As indicated above, the first heating elements (114) and the secondheating elements (116) are powered, such as by a power source (142). Thepower source (142) may be an electrical power source, when the heatingelements are resistive heating elements. The power source (142) may be aliquid heat source in the case that the heating elements are pipes orcapillaries through which a heated fluid may flow. In some embodiments,the power source (142) connects to a junction (not shown) printed orotherwise disposed on the heat blanket system (100) and in communicationwith the heating elements. In other embodiments, the power source (142)may be printed or otherwise directly disposed on the heat blanket system(100). The power source (142) may be a single source of power, such aselectricity or heated fluids, or may be multiple sources of power. Inthe case of a power source (142) based on electricity, the power source(142) may provide a constant current to both the first heating elements(114) and the second heating elements (116).

As an alternative embodiment, the first heating elements (114) and thesecond heating elements (116) may have the same spacings, or differentspacings shown. In this case, such as when the power source (142) is anelectrical power source, different currents may be applied to the firstheating elements (114) and/or the second heating elements (116). As aresult, differential heating may be accomplished by varying the powersupplied to the heating elements, rather than varying the spacingsbetween the heating elements.

As an alternative embodiment, heating elements may include additionalfeatures, such as including positive thermal coefficient self-regulationfeatures. Some printable heating materials have the capability toself-regulate to a predetermined temperature. In this manner, computercontrol or feedback might not be used to maintain the desiredtemperature within the heat blanket system (100) and/or patch.

The heat blanket system (100) may be provided with yet additionalfeatures. Thus, while FIG. 1 shows a configuration of components, otherconfigurations may be used without departing from the scope of theinvention. For example, various components may be combined to create asingle component. As another example, the functionality performed by asingle component may be performed by two or more components. Anadditional, more specific exemplary variation is described with respectto FIG. 4 through FIG. 7 .

FIG. 2 illustrates a method for manufacturing and using aprint-on-demand heat blanket system, in accordance with one or moreembodiments. The method shown in FIG. 2 may be implemented using theheat blanket system (100) shown in FIG. 1 . Steps shown with dashedlines may be considered optional in some embodiments.

As described with respect to FIG. 2 , a “manufacturing system” isrecited as performing the various steps. The “manufacturing system”refers to the computer, printer, and other hardware used to manufacturethe heat blanket system. Thus, the “manufacturing system” may includethe computer (500) of FIG. 1 and the three dimensional printer (506) ofFIG. 5 . In each step, the appropriate feature of the manufacturingsystem performs the specified act. Thus, for example, while thedescription of FIG. 2 refers to the “manufacturing system” performingthe step of receiving a digitized model, the actual step of receivingmay be performed by the computer (500). In another example,“manufacturing system” performing the step of printing may refer to anaction performed the three dimensional printer (506) shown in FIG. 5 .

At step 200, the manufacturing system receives a digitized model of atleast a portion of a composite structure having an inconsistency,wherein the digitized model includes a pre-calculated heating model thatspecifies areas of the inconsistency for which corresponding differentamounts of heating are applied to an uncured composite material that isapplied to the inconsistency. Thus, for example, a computer may receivethe digitized model of the composite structure and accompanyingpre-calculated heating model. An example of the heating model is shownwith respect to FIG. 13 and an example of a design for a heat blanketsystem is shown in FIG. 6 and FIG. 14B. In some embodiments, thecomputer may also generate the digitized model.

At step 202, the manufacturing system generates, from the digitizedmodel, a design heating elements of varying density across the areas.The design is configured to cause the heating elements to generate afirst amount of heat in a first sub-area in the areas. The design isfurther configured to cause the heating elements to generate a secondamount of heat in a second sub-area in the areas. The first amount ofheat is different than the second amount of heat, in order toaccommodate differential heating requirements in different sub-areas ofthe rework area.

At step 204, the manufacturing system prints, according to the design,the heating elements on a blanket to manufacture a heat blanket system.The term “blanket” (by itself) and “heat blanket system” aredifferentiated in that the “heat blanket system” is the “blanket,” afterthe heating elements designed according to the one or more embodimentshave been printed upon the blanket, along with any other componentsattached on or in the blanket.

Printing may be accomplished using a three dimensional printer loadedwith electrically resistive inks or other printing substances. Printingmay also be accomplished using deposition, screen printing, inkjetprinting, atomized jetted deposition, plasma flame spray, pastedeposition, and others. Other techniques may also be used to deposit orotherwise place the heating elements on the blanket.

The method of FIG. 2 may terminate thereafter. However, in otherembodiments, the method of FIG. 2 may include more steps.

For example, at step 206, the manufacturing system may print thermalsensors on the heat blanket system in corresponding ones of the areas.Printing thermal sensors may be accomplished using a three dimensionalprinter. However, pre-manufactured thermal sensors may also be attachedto the heat blanket system. Other devices may also be printed on theheat blanket system at this step (or some other step), such as but notlimited to a control circuit, an alert device, a wireless transmitter,etc.

In another example, at step 208, the manufacturing system reworks theinconsistency by applying the uncured composite material to theinconsistency. The uncured composite material may be applied by a robotapplying a composite patch, or liquid resin to the site of theinconsistency. Reworking may include removing some or all of thecomposite material at the site of the inconsistency. In some cases, ahuman may manually rework the inconsistency.

At step 210, the manufacturing system places the heat blanket system onthe uncured composite material after reworking. A robot or a humantechnician may place the heat blanket system on the inconsistency suchthat the appropriate sub-areas of the heat blanket system are overlaidthe corresponding modeled areas of the rework area.

At step 212, the manufacturing system cures the uncured compositematerial by causing the heating elements to produce heat. For example, acontrol circuit or computer may be used to apply electrical power toresistive heating elements. In this case, the method may also includeconnecting the resistive heating elements to an electrical power source,and applying electrical power to the resistive heating elements. In thecase that the heating elements are tubes, a heated liquid may be pumpedthrough the heating elements using a pump.

At step 214, the manufacturing system monitors, by the thermal sensors,corresponding temperatures in the areas. For example, a control circuitor a compute may monitor the temperature readings taken by the thermalsensors and then calculate a difference in the temperature readings.

At step 216, the manufacturing system then determines whether thetemperature difference exceeds a threshold. The threshold may varydepending on the particular procedure, but in an example the temperaturedifference threshold may be 10 degrees Fahrenheit (i.e., the differencein any two measured temperatures across the rework area is less than orequal to 10 degrees Fahrenheit).

If the temperature difference threshold is exceeded (a “yes”determination at step 216), then at step 218 the system may generate analert. In particular, the alert is generated when a first temperature ina first sub-area of the areas exceeds a second temperature in a secondsub-area in the by more than the threshold temperature difference. Thealert may be an audio, visual, or audiovisual alert that indicates to atechnician that the heating differential has exceeded the threshold.Thus, the technician may take action to reduce the temperaturedifferential across the rework area. Otherwise (a “no” determination atstep 216), the process proceeds to step 220.

At step 220, a determination is made whether the composite structure hasbeen cured. If not, (a “no” determination at step 220), then the processreturns to step 214 for monitoring and repeats. If curing is complete (a“yes” determination at step 220), then the process terminates.

FIG. 3 illustrates a method for reworking an aircraft using aprint-on-demand heat blanket system, in accordance with one or moreembodiments. The method of FIG. 3 may be characterized as a method ofreworking an aircraft including a composite material having an areaincluding an inconsistency. The method shown in FIG. 3 may beimplemented using the heat blanket system (100) shown in FIG. 1 , and/orthe devices shown in FIG. 5 . The method of FIG. 3 may be considered avariation of the method shown in FIG. 2 . Steps shown in dashed lines inFIG. 3 may be optional in some embodiments.

As described with respect to FIG. 3 , a “manufacturing system” isrecited as performing the various steps. The “manufacturing system”refers to the computer, printer, and other hardware used to manufacturethe heat blanket system. Thus, the “manufacturing system” may includethe computer (500) of FIG. 1 and the three dimensional printer (506) ofFIG. 5 . In each step, the appropriate feature of the manufacturingsystem performs the specified act. Thus, for example, while thedescription of FIG. 3 refers to the “manufacturing system” performingthe step of receiving a digitized model, the actual step of receivingmay be performed by the computer (500). In another example,“manufacturing system” performing the step of printing may refer to anaction performed the three dimensional printer (506) shown in FIG. 5 .

At step 300, the manufacturing system prepares the aircraft for reworkby preparing the composite material in the area of the inconsistency.Preparing the aircraft for rework may be performed by a robot or atechnician. The aircraft may be prepared by scarfing or sanding thecomposite material in the rework area, scoring the rework area, orcompletely removing a portion of the composite material in the reworkarea. Preparing the aircraft may also include creating or procuring acomposite patch to be placed in or on the rework area, and/or placing aliquid resin or pre-preg tape on the rework area.

At step 302, the manufacturing system generates a digitized model of thearea of the inconsistency. The digitized model includes a heating modelthat specifies sub-areas of the area of the inconsistency for whichcorresponding different amounts of heating are applied to an uncuredcomposite material that is applied to the inconsistency. An example of aheating model is shown in FIG. 13 .

At step 304, the manufacturing system generates, from the digitizedmodel, a design for heating elements of varying density across thesub-areas. The design is configured to cause the heating elements togenerate a first amount of heat in a first sub-area in the sub-areas.The design is further configured to cause the heating elements togenerate a second amount of heat in a second sub-area in the sub-areas.The first amount of heat is different than the second amount of heat. Adescription of an example of generating a design for heating elementsfrom the digitized model is described with respect to FIG. 8 throughFIG. 13 .

At step 306, the manufacturing system prints, according to the designusing a three dimensional printer, the heating elements on a blanket tomanufacture a heat blanket system. The term “blanket” (by itself) and“heat blanket system” are differentiated in that the “heat blanketsystem” is the “blanket,” after the heating elements designed accordingto the one or more embodiments have been printed upon the blanket, alongwith any other components attached on or in the blanket.

Optionally, at step 308, the manufacturing system may print a firstthermal sensor and a second thermal sensor on the heat blanket system aspart of manufacturing the heat blanket system. The first thermal sensoris printed on the heat blanket system to measure a first temperature inthe first sub-area of the rework area. The second thermal sensor isprinted on the heat blanket system to measure a second temperature inthe second sub-area of the rework area. Printing may be accomplishedusing a three dimensional printer, as shown in FIG. 5 .

At step 310, the manufacturing system applies an uncured composite patchto the area of the inconsistency. Applying may be performed by a robotor a human technician. The patch is an uncured composite material. Thepatch may be replaced, in some embodiments, with a liquid compositeresin or pre-preg tape. The one or more embodiments contemplate liquidcomposite resin or pre-preg tape as being considered equivalent to a“patch” for purposes of the one or more embodiments.

At step 312, the manufacturing system applies the heat blanket system tothe uncured composite patch. Application of the heat blanket system maybe accomplished using a robot, or by manual application by a humantechnician.

At step 314, the manufacturing system cures the uncured composite patchby applying differential heating to the uncured composite patch usingthe heat blanket system. Differential heating may be accomplished byapplying a uniform electrical current to different sub-sets of resistiveheating elements of varying density. Differential heating may also beaccomplished by applying different current levels to different sub-setsof resistive heating elements printed on the heat blanket system.

Optionally, at step 316, the manufacturing system may monitor, by thethermal sensors printed on the heat blanket system, correspondingtemperatures in the sub-areas of the rework area. For example, thesystem may measure, during curing, the first temperature with the firstthermal sensor. The system may also measure, during curing, the secondtemperature with the second thermal sensor. The system may thendetermine a difference between the first temperature and the secondtemperature, and monitor the difference over time.

At step 318, the manufacturing system may determine whether thedifference exceeds a temperature difference threshold. If thetemperature difference exceeds the threshold (a “yes” determination atstep 318), then at step 320, the system may generate an alert. If thealert is generated then, optionally, a robot or a technician may takeaction to moderate the difference between the first temperature and thesecond temperature. The action may be to temporarily suspend heating ofsome or all of the rework area, to add insulation or remove insulationfrom some or all of the rework area (either above or below the heatblanket system), to modulate an amount of electrical power beingdelivered to the heat blanket system, to modulate the flow rate of aheated liquid being sent through heating element pipes, or a variety ofother possible actions.

Returning to FIG. 3 , whether or not the alert is generated at step 320(e.g., a “no” determination at step 318 or after generation of the alertat step 320), then at step 322 a determination is made whether thecomposite patch has cured. If the composite patch has not completedcuring (a “no” determination at step 322), then the method returns tostep 316 and repeats. Otherwise (a “yes” determination at step 322) themethod of FIG. 3 terminates.

While the various steps in the flowcharts shown in FIG. 2 and FIG. 3 arepresented and described sequentially, one of ordinary skill willappreciate that some or all of the steps may be executed in differentorders, may be combined or omitted, and some or all of the steps may beexecuted in parallel. Furthermore, the steps may be performed activelyor passively.

The following example shown in FIG. 4 through FIG. 7 is for explanatorypurposes only and not intended to limit the scope of the invention. FIG.4 through FIG. 7 should be considered together.

FIG. 4 illustrates a section of a composite material object, including arework area, in accordance with one or more embodiments. As shown inFIG. 4 , a composite part (400) is being reworked. The composite part(400) includes a rework area (402) in which there existed aninconsistency. Because a portion of the rework area (402) has beenremoved from the composite part (400), the inconsistency is not shown inFIG. 4 . A composite patch (404) is being applied to the rework area(402) in order to rework the composite part (400), thereby effectivelymitigating the previously present inconsistency. In differentembodiments the composite patch (404) may take the form of liquidcomposite resin or pre-preg tape, or other composite materials.

The rework area (402) includes three sub-areas in this example: firstsub-area (406), second sub-area (408), and third sub-area (410). Becausethe sub-areas vary in thickness relative to each other, the compositepatch (404) may require different amounts of heating in order tomaintain a uniform temperature differential throughout the compositepatch (404). The heat blanket system (100) described with respect toFIG. 1 , and below with respect to FIG. 5 through FIG. 7 may be used toheat the composite patch (404) at a temperature differential that varieswithin a pre-determined temperature threshold.

FIG. 5 illustrates a system for generating a print-on-demand heatblanket system, in accordance with one or more embodiments. The systemshown in FIG. 5 may be used to manufacture the heat blanket system (100)shown in FIG. 1 using the methods described with respect to FIG. 2 andFIG. 3 . Thus, the system shown in FIG. 4 may be used to generate thecomponents used to rework the composite part (400) shown in FIG. 4 .

The system shown in FIG. 4 includes a computer (500). The computer (500)may be a laptop computer, desk top computer, tablet computer, mobilephone, or other computing device.

The computer (500) includes software which, when executed by a processorusing data describing the rework area and the composite part beingreworked, generates a heat model (502). The heat model (502) describesthe differential heating predicted in different sub-areas of thecomposite part in order to maintain a temperature differential,throughout the composite patch, within the acceptable threshold. Thus,for example, referring to FIG. 4 , the heat model (502) may describe afirst temperature to be applied to the first sub-area (406), a secondtemperature to be applied to the second sub-area (408), and a thirdtemperature to be applied to the third sub-area (410) such that thecomposite patch (404) will maintain a constant temperature (within theacceptable temperature differential threshold) throughout the compositepatch (404) during the curing process. An example of the heat model(502) is shown as heat model (1300) in FIG. 13 .

The computer (500) also includes software which, when executed by aprocessor using data describing the rework area, the composite partbeing reworked, and the heat model (502), generates a blanket design(504). Thus, the blanket design (504) is a data structure containingdata that is stored in a non-transitory computer readable storagemedium. The blanket design (504) specifies the location, shape, anddensity of heating elements disposed in various sub-areas of the heatblanket system. Thus, the blanket design (504) may describe, forexample, the arrangement of parts of the heat blanket system (100) shownin FIG. 1 or the heat blanket system shown in FIG. 6 . An example of ablanket design (504) is described with respect to FIG. 14A and FIG. 14B.

The blanket design (504) may be provided to a three dimensional printer(506). The three dimensional printer (506) may use resistive inks toprint electrically resistive heating elements on the heat blanket system(508). The three dimensional printer (506) may also print threedimensional tubes on the heat blanket system (508) in order to createfluid channels through which a heating fluid may be pumped during thecuring process. The heating elements may take other forms, as well.Additionally, as indicated above, other types of printers or depositiondevices may be used other than a three dimensional printer.

The three dimensional printer (506) may print other aspects of the heatblanket system (508) as well. For example, the three dimensional printer(506) may print or build up the substrate upon which the heatingelements are printed. The three dimensional printer (506) may print orbuild up layers of dielectric or insulative laminate materials on one orboth sides of the substrate. The three dimensional printer (506) mayalso print or apply other devices, such as but not limited to thermalsensors, thermocouples, control circuits, alert devices, power systems,gas sensors, and other types of features, and may also punchperforations in the heat blanket system (508).

Other devices may be used in addition to the three dimensional printer(506). For example, prior to use of the three dimensional printer (506),a machine may be used to cut the substrate from stock. The stocksubstrate may be fed to the three dimensional printer (506) in order toprint the heating elements on the substrate. The substrate with heatingelements may then be provided to a lamination machine in order tolaminate one or both sides of the substrate. Additional machines may addadditional features or devices to the heat blanket system (508), or maystrip certain sub-areas of the heat blanket system (508) of previouslybuilt up layers. Thus, the one or more embodiments contemplate that morethan just the three dimensional printer (506) may be present in thesystem shown in FIG. 5 .

In any case, the system shown in FIG. 5 manufactures the heat blanketsystem (508). The heat blanket system (508) may then be used to applyheat to a composite patch placed at a rework area, as shown for examplein FIG. 6 .

FIG. 6 illustrates a specific example of a print-on-demand heat blanketsystem, and a method of use, in accordance with one or more embodiments.FIG. 7 illustrates application of the specific example of theprint-on-demand heat blanket system shown in FIG. 6 , in accordance withone or more embodiments. FIG. 6 and FIG. 7 should be viewed together asa whole. Thus, FIG. 6 and FIG. 7 share common reference numerals.

The example shown in FIG. 6 and FIG. 7 is a variation of the heatblanket system (100) shown in FIG. 1 and the methods shown in FIG. 2 andFIG. 3 . The example shown in FIG. 6 and FIG. 7 may be applied to thecomposite part (400) shown in FIG. 4 using the heat blanket system (508)manufactured as described with respect to FIG. 5 .

In the example shown, a composite structure (600) is a part of anaircraft fuselage or wing. Thus, for example, the composite structure(600) includes a skin (602) formed from a composite material supportedby multiple stiffening elements, such as stiffening element (604) andstiffening element (606). The stiffening elements act as heat sinks;i.e., the stiffening elements absorb more heat applied to the skin (602)relative to portions of the skin (602) under which stiffening elementsare not present.

An inconsistency (700) is present in the skin (602) of the compositestructure (600). Initially, a technician has been tasked with mitigatingthe inconsistency (700).

Initially, technician prepares the composite structure (600) for reworkby defining a rework area (702). The rework area (702) is indicated bythe marked line. The technician removes composite material from the skin(602) in the rework area (702) and prepares a pre-preg patch (704)having a shape and dimensions consistent with the rework area (702). Thepre-preg patch (704) is a composite material, or layers of compositematerial, pre-impregnated with a liquid resin. The technician appliesthe pre-preg patch (704) to the rework area (rework area (702)).

The technician measures that the pre-preg patch (704) is thicker betweenthe first stiffening element (604) and the second stiffening element(606), relative to outer portions of the pre-preg patch (704). Thetechnician also notes that the first stiffening element (604) and thesecond stiffening element (606) will act as heat sinks during theprocess of curing the pre-preg patch (704).

Thus, the technician enters data regarding the composite structure(600), the rework area (702), and the pre-preg patch (704) into a heatmodeler software on a computer in order to generate a heat model (1300).The heat modeler software may query an existing model-based definitionof the structure based on the rework location coordinates and partnumber. The heat model (1300) takes into account the thermodynamicproperties of the skin (602), the first stiffening element (604), thesecond stiffening element (606), and the pre-preg patch (704). The heatmodel (1300) also takes into account the effect of differentialthickness of the pre-preg patch (704) along the length of the pre-pregpatch (704). The heat model (1300) indicates that a first specificamount of heat should be applied to the rework area (702) in the areasof the first stiffening element (604) and the second stiffening element(606), a second specific amount of heat should be applied to the centerof the pre-preg patch (704) where the pre-preg patch (704) is thickest,a third specific amount of heat at the edges of the pre-preg patch(704), and a fourth specific amount of heat at other locations of thepre-preg patch (704). The heat model (1300) indicates a heating patternthat, if applied to the pre-preg patch (704), will result in a constanttemperature throughout the pre-preg patch (704) during curing, at leastwithin an acceptable temperature threshold.

The heat model (1300) is provided as input to a design software moduleon the computer in order to generate a print design. The design softwaremodule outputs a design for a pattern of resistive heating elements(608) on a heat blanket system (610). The design also includes a seriesof perforations, such as perforation (612), through which gasses thatarise during curing may escape from the pre-preg patch (704).

The print design shows four different sub-areas of the heat blanketsystem (610) with different densities of the resistive heating elements(608). For example, a first sub-area (614) is disposed around the edgesof the heat blanket system (610). The density of the resistive heatingelements (608) is higher in the first sub-area (614) relative to thedensity of the resistive heating elements (608) in a second sub-area(616) just inside the edges where the skin (602) will be present but thefirst stiffening element (604) and the second stiffening element (606)will not be present. However, the highest density of the resistiveheating elements (608) is placed in the third sub-area (618) and thefourth sub-area (620), because these sub-areas correspond to thelocation where the first stiffening element (604) and the secondstiffening element (606) (which act as heat sinks) will be located. Theprint design also shows a junction (622) to which a power source (624)may be placed.

The technician then provides the print design to a three dimensionalprinter, such as the three dimensional printer (506) shown in FIG. 5 .The three dimensional printer optionally prints the substrate, or thesubstrate for the heat blanket system (610) may be provided. The threedimensional printer prints the resistive heating elements (608) onto thesubstrate. The three dimensional printer also may print laminationlayers over the resistive heating elements (608). The result is acustom, printed-on-demand heat blanket system available for use for thespecific rework project the technician has been tasked to accomplish.

The technician then places the heat blanket system (610) on the reworkarea (702) over the pre-preg patch (704). As shown by the dotted lines,such as dotted line (706), the different sub-areas of the heat blanketsystem (610) identified above overlay the specific areas of the reworkarea (702) that will have different thermodynamic properties. Forexample, the third sub-area (618) and the fourth sub-area (620) overlaythe heat sinks caused by the first stiffening element (604) and thesecond stiffening element (606), respectively. The first sub-area (614)overlays the edges of the rework area (702). The second sub-area (616)overlays areas that cover the skin (602) away from the edges of therework area (702) and also away from the first stiffening element (604)and the second stiffening element (606). In other words, the respectivedensities of the resistive heating elements (608) specifically match thethermodynamic profile (heat model (1300)) of the rework project whichthe technician has been tasked to perform.

The technician turns on the power source (624), which provides aconstant source of electrical current to the resistive heating elements(608). Due to the varying density of the resistive heating elements(608) in the different sub-areas of the heat blanket system (610), theheat blanket system (610) produces differing amounts of heat todifferent areas of the pre-preg patch (704).

As a result, even though heat sinks and thermodynamic edge effects couldhave resulted in variable temperatures throughout the length of thepre-preg patch (704), the pre-preg patch (704) is maintained at aconstant temperature throughout the length of the pre-preg patch (704),within a specified engineering tolerance.

The cure process may be monitored, such as by monitoring thetemperatures of the different sub-areas of the pre-preg patch (704) inthe rework area (702). In this case, the temperature remains constantthroughout the pre-preg patch (704), within plus or minus ten degreesFahrenheit, for the four hours used to cure the pre-preg patch (704).When the cure process is complete, the heat blanket system (610) isremoved from the rework area (702), the rework process is completed, andthe inconsistency (700) has been mitigated.

In summary, the composite structure (600) being reworked has a skin withintegral I-beam stiffening elements. The scarf rework on the skinsurface passes over the flanges of two I beam stiffeners. The part modelfor this location on the structure was interrogated and a thermalanalysis performed, showing that a higher heat density is to be appliedin the rework locations that are common to the stringer flanges. The“skin-only” areas between the stiffeners require a lower heatingdensity. The edges of the heat blanket system require a higher heatdensity to compensate for the heat losses at the edges of the heatblanket system.

A Thermal Analysis Module (TAM) (the software which produces the heatmodel (502) in FIG. 5 or the heat model (1300) in FIG. 13 ) calculatesthe heat density to be used to achieve a uniform isothermal conditionfor the part being reworked. The heat density data is exported to aBlanket Design Module (BDM) (the software which produces the blanketdesign (504) in FIG. 5 or the heat density map (1400) and correspondingblanket design described with respect to FIG. 14 ). The BDM determinesthe watt density to achieve a uniform temperature during the curingprocess.

The desired watt densities are achieved by varying the spacing of theresistive heating wires. Areas of the structure requiring higher heatdensities have the heating elements placed more closely together. Areasrequiring less heat have the heating elements spaced further apart. Thespacing of these heating elements are defined by the BDM.

The circuitry is printed or deposited onto a thin flexible film such aspaper, KAPTON®, or fiberglass. The circuit array is then passed througha laminator to encapsulate and insulate the electrical traces. Thecircuit traces are terminated with a standard power input cable.

The heat blanket system is connected to a controller and used to cure acomposite material. The heat blanket system has the heat output densitymatched exactly to the heat density requirements of the compositestructure (600) being reworked. In short, the heat blanket system (610)is custom designed for the specific application thermal uniformity ofthe curing, but is manufactured on-site and thus may be considered a“print-on-demand” heat blanket system.

FIG. 8 through FIG. 14B should be considered together. FIG. 8 throughFIG. 14B show a specific example of producing a design for heatingelements that are to be printed on a heat blanket system, with thedesign produced using a heating model. Thus, FIG. 8 through FIG. 14Bshow a specific example of how a custom heat blanket system may bedesigned and produced from a heating model, with the heat blanket systemfor use on a specific rework project to be performed on a particularaircraft panel. Thus, FIG. 8 through FIG. 14B may share common referencenumerals which refer to common objects having common descriptions.

The example shown in FIG. 8 through FIG. 14B does not necessarily limitthe other examples described herein, or the claimed inventions, as otherexamples are possible. Any numerical values, shapes, designs, etc. maybe varied according to various different projects or embodiments.

Attention is first turned to FIG. 8 through FIG. 10 . FIG. 8 illustratesan aircraft panel (800) having with a rework area (802) including aninconsistency (804), in accordance with one or more embodiments. FIG. 8may be characterized as an outer mold line of the aircraft panel (800).The aircraft panel (800) is formed of a composite material. Theinconsistency (804) is to be reworked using a process which involvescuring a composite patch, composite liquid or gel, a pre-preg patch, orother composite material for which heat is applied to cure the reworkarea.

FIG. 9 illustrates an alternative view of the aircraft panel (800) ofFIG. 8 , in accordance with one or more embodiments. In particular, FIG.9 shows an opposing side of the aircraft panel (800) shown in FIG. 8 ,and thus may be characterized as an inner mold line of the aircraftpanel (800).

The inner mold line shows a number of stiffeners that run a length ofthe aircraft panel (800), such as stiffener (900) and stiffener (904).The stiffeners are hollow in this example, but need not be hollow. Thestiffeners in this particular example may be characterized as “hatshaped” stiffeners or characterized as “omega stiffeners.” Thestiffeners can have different shapes in different embodiments.

The inner mold line also shows a number of frame elements, includingframe element (906) and frame element (908). Each frame element may be asolid material, including aluminum, composite materials, etc., usefulfor stiffening the aircraft panel (800) in a hoop direction of theaircraft panel (800). However, the frame elements may also be hollow,and have a variety of different shapes, and may be composed of a varietyof different materials.

FIG. 10 illustrates a cross-section of the aircraft panel (800) of FIG.8 , in accordance with one or more embodiments. The aircraft panel (800)is shown as a skin. A frame element, in this case the frame element(906), is shown connected to the aircraft panel (800) at a skin-to-frameinterface (1000). The stiffener (900), also connected to the aircraftpanel (800) along two flanges, including flange (1002) and flange (1004)of the stiffener (900), is shown passing underneath the frame element(906). The stiffener (900) may be, or may not be, connected to the frameelement (906). A cavity (1006) is disposed inside the stiffener (900),and may run the length of the stiffener (900).

A heat blanket system (1008) is shown for reference. The heat blanketsystem (1008) is the custom heat blanket system designed as describedwith respect to FIG. 14A and FIG. 14B.

FIG. 11 illustrates a part of a heating simulation as part of a processfor producing a heating model for the panel shown in FIG. 8 , inaccordance with one or more embodiments. FIG. 12 illustrates anotherpart of the heating simulation in FIG. 11 as part of a process forproducing a heating model for the panel shown in FIG. 8 , in accordancewith one or more embodiments.

Thermal analysis was conducted on a simulated panel (1100), whichcorresponds to the aircraft panel (800) shown in FIG. 8 through FIG. 10. The simulated panel (1100) also has simulated stiffeners, such assimulated stiffener (1102), which correspond to the stiffeners shown inFIG. 8 through FIG. 10 . The model also included simulated frameelements, such as simulated frame element (1104), corresponding to theframe elements shown in FIG. 8 through FIG. 10 .

The gauge, or thickness, of the aircraft panel (800) is constant.However, the thermal load varies by a large degree for the followingreasons. The closed hat stringer cavity (1006) creates an insulating airgap inside the stringer cavity (1006) that prevents convective heatloss. This area will trap heat and create a localized hot spot on theouter skin common to the stringer cavity (1006). Meanwhile, the hatstringer flanges, such as flange (1002) and flange (1004), that overlaythe aircraft panel (800) increase the skin thickness locally, creating aheat sink directly adjacent to the insulating air gap created by thestringer cavity (1006). Further complicating matters are the frameattachments points, characterized by the skin-to-frame interface (1000),between hat stringers. The frame attachment shear ties (i.e., theskin-to-frame interface (1000)) span the gap between each hat stringerat every frame location. Each frame attachment location is a localizedheat sink of about two by six inches, in this specific embodiment.

Returning to FIG. 11 , a first simulation area (1106) is centered overthe stringer cavity (1006) in the longitudinal direction. The firstsimulation area (1106) corresponds to the rework area (802). The frameelement (906) spans the simulation area (1106) near the right edge.

Returning to FIG. 12 , a second simulation area (1108) shows convectiveheat losses that occur when simulated heating is applied to the firstsimulation area (1106). Together, the first simulation area (1106) andthe second simulation area (1108) form a heating simulation.

The heating simulation may factor other conditions. For example, theheating simulation may also factor in the insulating properties of thevacuum bagging materials used in a composite cure process.

During a rework simulation, the first simulation area (1106) wasvirtually heated using the heat energy equivalent to a five watt persquare inch resistive heat blanket system. The duty cycle of thesimulated heat source was modulated to achieve a maximum temperature of360° Fahrenheit anywhere within the bounds of the first simulation area(1106). This level of power was maintained until all the temperaturechanges within the first simulation area (1106) were about zero.

FIG. 13 illustrates a heating model for the aircraft panel (800) shownin FIG. 8 , in accordance with one or more embodiments. FIG. 13 showsthe results of the heating simulation performed with respect to FIG. 11and FIG. 12 , and thus FIG. 13 shows an example of a heating model(1300).

The resulting simulation temperatures are depicted in spans of contouredlines within the rework area (1302), with each span indicating atemperature differential of about 20 degrees Fahrenheit. A temperaturescale (1304) is shown for reference. Hashing patterns within the spansshow different temperature ranges, from the hottest areas (about 360°F.˜340° F.) to the coolest areas (about room temperature (70° F.)), asindicated by the hashing patterns shown for which the temperature scale(1304) provides a legend.

Line (1306), running from left to right in FIG. 13 , follows the hatstringer cavity (1006). Line (1308), running from top to bottom in FIG.13 , follows the fuselage frame. The central portion of the rework area(1302), common to the stringer cavity (1006), was the hottest region.However, the profound heat sink effect of the skin-to-frame interface(1000) (again, indicated by line (1308)) is clearly visible in area(1310) on the right side of the rework area (1302).

The data from the initial test is used define discrete temperature bandsor zones for the rework area (1302). The dimensional coordinates ofthermal zones are defined by the thermal analysis module (TAM) on thepart model. Iterative thermal simulations can then be performed by theTAM. The simulated heat output (watts per square inch) is independentlyincreased or decreased within in each zone. This loop is repeated untilthe desired degree of thermal uniformity is achieved within the reworkarea (1302).

The final output of the TAM is a heat density map for a heat blanketsystem based on the thermal analysis of the structure's model baseddefinition and the location of the inconsistency on the aircraft panel(800). An example of a heat density map for a heat blanket system isshown in FIG. 14 below.

FIG. 14A and FIG. 14B illustrate different views of a heat density mapfor a heat blanket system generated from the heating model in FIG. 13 ,in accordance with one or more embodiments. The heat density map (1400)for the heat blanket system is a guide for determining the density ofheating elements to be placed in each corresponding area of the heatdensity map (1400). In particular, the spacing of heating elements maybe inferred from the particular number of Watts of heating to be appliedto a particular area. Thus, FIG. 14A and FIG. 14B effectively show adesign, generated using the heating model of FIG. 13 , for heatingelements to be printed on a heat blanket system that is to be applied tothe aircraft panel (800).

The heat density map (1400) includes different zones, such as Zone A(1402), Zone B (1404), Zone C (1406), and Zone D (1408). Each zone isshown by a different hash pattern. Each zone is to receive a pre-definednumber of Watts of heat energy. The heat blanket system is to apply 8Watts of heat energy in Zone A (1402). The heat blanket system is toapply 6 Watts of heat energy in Zone B (1404). The heat blanket systemis to apply 4 Watts of heat energy in Zone C (1406). The heat blanketsystem is to apply 3 Watts of heat energy in Zone D (1408). Taken incombination as a whole, when the above pattern of heat energies areapplied by the customized heat blanket system to the rework area (802),the net resulting temperature achieved in the rework area (802) is aboutuniform (i.e., within a pre-determined temperature threshold).Accordingly, the pre-preg patch or other composite material used torework the inconsistency (804) maintains a uniform temperaturethroughout the cure process, despite fact that differentials in thermalabsorptivity exist within the rework area (802).

Note that once the size, shape, and heat densities for each zone aredefined, the heating model data can be output to a circuit design moduleto design the circuit traces for printing of the heat blanket systemsuch that, when powered, the circuit traces will produce the designatednumber of Watts of heat energy. At this stage, the heat density zonesmay be edited for improved manufacturing according to user input. If thechanges are deemed significant, the resulting producible design can bere-run through the TAM module to ensure the changes do not affect theperformance of the heat blanket system to an undesirable degree.

Thus, the one or more embodiments described above provide for aprint-on-demand (POD) heat blanket system (printable by direct writecircuitry, and inkjet printers, or three dimensional printers). When apart is to be reworked, a model based definition for that part can bequeried to know the exact composition of the part at the location of theinconsistency, along with any attached substructure or systems. Knowingthe composition of the part, and substructure, a Finite Element Analysis(FEA) can be performed to determine the amount of heat energy to beapplied to heat a region of interest (ROI) to uniform temperature. Theheating requirements can be modeled like any other property of the ROI,much like stress or strain. Given this heat flow and heat density data,custom heating circuitry can be designed and printed on a heat blanketsystem in order to uniformly heat a ROI even though the thermalrequirements of the part vary greatly across the ROI. For example, if aROI has a localized area of reinforcement plies, the custom circuitrywould have a corresponding area where the resistance wires are spacedvery closely together to achieve a higher heat density in that specificarea. Meanwhile, other areas with thin skins would have the resistivewires spaced farther apart to avoid overheating in those locations.

The following is a summary of an exemplary process flow for an aircraft.

1) The location and size/depth of the inconsistency is defined in anaircraft coordinate location.

2) The inconsistency definition data is input into Thermal AnalysisModule (TAM).

3) The TAM queries the part Model Based Definition (MBD) to determinethe part composition in the region of interest.

4) The TAM calculates the amount of heat energy/density to be appliedfor the areas of the ROI to achieve an isothermal hold for desiredrework cure temperature.

5) TAM exports the heat density data to the Blanket Design Module (BDM).

6) The BDM designs the circuitry for the heat blanket system withvariable wire spacing to achieve uniform heating of the ROI based on thespecific part MBD.

7) The BDM determines the optimal locations for temperature sensors andincorporates those into the design.

8) The BDM outputs a sensor design to a printer.

9) The printer prints circuits and sensors onto a thermallyresistant/flexible print medium to form the heat blanket system.

10) Electrical terminations are made on the heat blanket system.

11) Circuits are run through a laminator to encapsulate and insulatecircuitry for use.

12) Power and sensor cables are added to the heat blanket system.

13) The heat blanket system is placed on ROI per location instructions.

14) The cure process is executed.

15) The heat blanket system is disposed of, recycled, or stored.

FIG. 15 illustrates an aircraft manufacturing and service method, inaccordance with one or more embodiments. FIG. 16 illustrates anaircraft, in accordance with one or more embodiments. FIG. 15 and FIG.16 should be considered together. The methods and systems described withrespect to FIG. 1 through FIG. 9 may be used in the context of theaircraft manufacturing and service method (1500) shown in FIG. 15 .Similarly, the methods and system described with respect to FIG. 1through FIG. 9 may be used to rework portions of the aircraft (1600)shown with respect to FIG. 16 .

Turning to FIG. 15 , during pre-production, the exemplary aircraftmanufacturing and service method (1500) may include a specification anddesign (1502) of the aircraft (1600) in FIG. 16 and a materialprocurement (1504) for the aircraft (1600). During production, thecomponent and subassembly manufacturing (1506) and system integration(1508) of the aircraft (1600) in FIG. 16 takes place. Thereafter, theaircraft (1600) in FIG. 16 may go through certification and delivery(1510) in order to be placed in service (1512). While in service by acustomer, the aircraft (1600) in FIG. 16 is scheduled for routinemaintenance and service (1514), which may include modification,reconfiguration, refurbishment, and other maintenance or service.

Each of the processes of the aircraft manufacturing and service method(1500) may be performed or carried out by a system integrator, a thirdparty, and/or an operator. In these examples, the operator may be acustomer. For the purposes of this description, a system integrator mayinclude, without limitation, any number of aircraft manufacturers andmajor-system subcontractors; a third party may include, withoutlimitation, any number of venders, subcontractors, and suppliers; and anoperator may be an airline, leasing company, military entity, serviceorganization, and so on.

With reference now to FIG. 16 , an illustration of an aircraft (1600) isdepicted in which an advantageous embodiment may be implemented. In thisexample, the aircraft (1600) is produced by the aircraft manufacturingand service method (1500) in FIG. 15 . The aircraft (1600) may includeairframe (1602) with systems (1604) and an interior (1606). Examples ofsystems (1604) include one or more of a propulsion system (1608), anelectrical system (1610), a hydraulic system (1612), and anenvironmental system (1614). Any number of other systems may beincluded.

Although an aerospace example is shown, different advantageousembodiments may be applied to other industries, such as the automotiveindustry. Thus, for example, the aircraft (1600) may be replaced by anautomobile or other vehicle or object in one or more embodiments.

The apparatus and methods embodied herein may be employed during any oneor more of the stages of the aircraft manufacturing and service method(1500) in FIG. 15 . For example, components or subassemblies produced inthe component and subassembly manufacturing (1506) in FIG. 15 may befabricated or manufactured in a manner similar to components orsubassemblies produced while the aircraft (1600) is in service (1512) inFIG. 15 .

Also, one or more apparatus embodiments, method embodiments, or acombination thereof may be utilized during production stages, such asthe component and subassembly manufacturing (1506) and systemintegration (1508) in FIG. 15 , for example, by substantially expeditingthe assembly of or reducing the cost of the aircraft (1600). Similarly,one or more of apparatus embodiments, method embodiments, or acombination thereof may be utilized while the aircraft (1600) is inservice (1512) or during maintenance and service (1514) in FIG. 15 .

For example, one or more of the advantageous embodiments may be appliedduring component and subassembly manufacturing (1506) to reworkinsistencies that may be found in composite structures. As yet anotherexample, one or more advantageous embodiments may be implemented duringmaintenance and service (1514) to remove or mitigate inconsistenciesthat may be identified. Thus, the one or more embodiments described withrespect to FIG. 1 through FIG. 9 may be implemented during component andsubassembly manufacturing (1506) and/or during maintenance and service(1514) to remove or mitigate inconsistencies that may be identified.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

What is claimed is:
 1. A heat blanket system comprising: a blanketcomprising a first sub-area and a second sub-area; and a plurality ofheating elements printed on the blanket, wherein: first spacings betweenfirst ones of the plurality heating elements in the first sub-areavaries relative to second spacings between second ones of the pluralityof heating elements in the second sub-area, the first spacings and thesecond spacings vary according to a design, the design is configured foruse on a uniquely defined rework area on a uniquely defined compositematerial object comprising a third area comprising a heat sink regionand a fourth area comprising a non-heat sink region, the first sub-areais sized and dimensioned to be placed over the third area, and thesecond sub-area is sized and dimensioned to be placed over the fourtharea.
 2. The heat blanket system of claim 1, wherein the first spacingsare less than the second spacings.
 3. The heat blanket system of claim1, further comprising: a power source connected to the plurality ofheating elements.
 4. The heat blanket system of claim 3, wherein theplurality of heating elements comprise resistive heating elements, thepower source comprises a single source of electricity, and the powersource is configured to apply an about constant current to the pluralityof heating elements.
 5. The heat blanket system of claim 1, wherein theblanket further comprises a plurality of perforations disposed throughthe blanket.
 6. The heat blanket system of claim 1, further comprising:a thermal sensor printed on the blanket.
 7. The heat blanket system ofclaim 6, further comprising: a wireless transmitter connected to thethermal sensor; and a control circuit printed on the blanket, thecontrol circuit configured to modify power delivered to the plurality ofheating elements based on signals received by the wireless transmitter.8. The heat blanket system of claim 1, wherein: the blanket comprisespaper or polyethylene terephthalate (PET), and the plurality of heatingelements comprise conductive or resistive inks.
 9. The heat blanketsystem of claim 8, wherein the blanket further comprises: a firstdielectric layer disposed on a first side of the paper or PET, and asecond dielectric layer disposed on a second side of the paper or PET,opposite the first side.
 10. The heat blanket system of claim 1, furthercomprising: a first thermal sensor printed on the blanket in the firstsub-area; and a second thermal sensor printed on the blanket in thesecond sub-area.
 11. The heat blanket system of claim 10, furthercomprising: a wireless transmitter connected to the first thermal sensorand the second thermal sensor; and a control circuit printed on theblanket, the control circuit configured to modify power delivered to theplurality of heating elements based on signals received by the wirelesstransmitter.
 12. The heat blanket system of claim 10, furthercomprising: a wireless transmitter connected to the first thermal sensorand the second thermal sensor; an alert device connected to the wirelesstransmitter; and a control circuit printed on the blanket and incommunication with the wireless transmitter and the alert device, thecontrol circuit programmed to cause the alert device to issue an alertwhen a difference in temperature measured by the first thermal sensorand the second thermal sensor exceeds a threshold.
 13. The heat blanketsystem of claim 10, further comprising: a wireless transmitter connectedto the first thermal sensor and the second thermal sensor; an alertdevice connected to the wireless transmitter; and a control circuitprinted on the blanket and in communication with the wirelesstransmitter and the alert device, the control circuit programmed to:cause the alert device to issue an alert when a difference intemperature measured by the first thermal sensor and the second thermalsensor exceeds a threshold, and modify power delivered to the pluralityof heating elements based on signals received by the wirelesstransmitter.
 14. The heat blanket system of claim 10, furthercomprising: a computer printed on the blanket and programmed to: monitora first temperature of the first sub-area, monitor a second temperatureof the second sub-area, and control a first amount of power deliveredfrom a power source to first heating elements, of the plurality ofheating elements, in the first sub-area, control a second amount ofpower delivered from the power source to second heating elements, of theplurality of heating elements, in the second sub-area, wherein the firstamount of power is different than the second amount of power.
 15. Theheat blanket system of claim 1, wherein the blanket comprises aplurality of perforations disposed through a third sub-area of theblanket, and wherein the third sub-are is disposed between the firstsub-area and the second sub-area.
 16. The heat blanket system of claim1, wherein the first sub-area is disposed at a perimeter of the blanket,and wherein the second sub-area is disposed inside the first sub-area.17. The heat blanket system of claim 1, wherein: the first sub-area islocated on the blanket such that the first sub-area covers reworklocation coordinates of a pre-defined rework area when the blanket isdisposed on the pre-defined rework area, and the second sub-area islocated on the blanket such that the second sub-area lies outside therework location coordinates of the pre-defined rework area when theblanket is disposed on the pre-defined rework area.
 18. The heat blanketsystem of claim 17, wherein: the rework location coordinates correspondto a stiffening element connected to the pre-defined rework area, andthe first spacings of the plurality heating elements in the firstsub-area are less than the second spacings of the plurality of heatingelements in the second sub-area.
 19. A heat blanket system comprising: ablanket comprising: a perimeter area, a first outside area definedwithin the perimeter area, a first middle area defined within theperimeter area to one side of the first outside area, a central areadefined within the perimeter area to one side of the first middle area,a second middle area defined within the perimeter area to one side ofthe central area opposite the first middle area, and a second outsidearea defined within the perimeter area to one side of the second middlearea opposite the central area; a first set of heating elements printedon the perimeter area, the first set of heating elements having firstspacings; a second set of heating elements printed on the first outsidearea, the second set of heating elements having second spacings; a thirdset of heating elements printed on the first middle area, the third setof heating elements having third spacings; a fourth set of heatingelements printed on the central area, the fourth set of heating elementshaving fourth spacings; a fifth set of heating elements printed on thesecond middle area, the fifth set of heating elements having fifthspacings; and a sixth set of heating elements printed on the secondoutside area, the sixth set of heating elements having sixth spacings,wherein at least two of the first spacings, the second spacings, thesecond spacings, the third spacings, the fourth spacings, the fifthspacings, and the sixth spacings are different than each other.
 20. Aheat blanket system comprising: a blanket; a first plurality of heatingelements printed on a first sub-area of the blanket, wherein the firstplurality of heating elements comprises first spacings between the firstplurality of heating elements; and a second plurality of heatingelements printed on a second sub-area of the blanket, wherein the secondplurality of heating elements comprises second spacings between thesecond plurality of heating elements, wherein the first spacings and thesecond spacings are sized and dimensioned differently according to aheat density map defined for a rework area to which the blanket isapplicable.